MCQs Questions on Krebs Cycle

MCQs Questions on Krebs Cycle

Krebs Cycle An Aerobic Respiration – Definition


Krebs Cycle is an aerobic respiration took place in the mitochondria of living cell. The end-product of glycolysis which is pyruvate is entered into Krebs cycle or citric acid cycle. The NADH goes to the electron transport chain. During aerobic metabolism, free oxygen accepts electrons and reduces to water. The aerobic respiration is organized into a number of reactions. Each reaction is catalyzed by a specific enzyme.


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The MCQs questions on “Krebs Cycle An Aerobic Respiration”, will help you to understand the evolution of aerobic respiration, and detailed Krebs Cycle Steps in the form of MCQs. All the MCQs about Krebs Cycle An Aerobic Respiration are published according to the new study syllabus for academic year 2021-22.

Table of Contents:

  • Evolution of aerobic respiration
  • Krebs cycle steps

All of these MCQs on “Krebs Cycle An Aerobic Respiration” in Zoology MCQs are preferably for test / interview preparation for BSc, MSc, BS (Hons), NTS, FPSC, PPSC, PTS, CSS, MDCAT, ECAT, MCAT and all other competitive examination also for foreign study including overseas students.


MCQs on Krebs Cycle (Questions and Answers)


𓇼 Evolution of Aerobic Respiration:

Q1. Which product of glycolysis still contain large amount of energy?

  1. Glucose-6-phosphate
  2. Fructose-6-phosphate
  3. Pyruvate
  4. none

Answer: c

Q2. In which cell component, the evolution of aerobic respiration took place?

  1. Mitochondria
  2. Ribosomes
  3. Cytoplasm
  4. Vacuole

Answer: a

Q3. The evolution of which respiration has made the organism efficient?

  1. Anaerobic respiration
  2. Aerobic respiration
  3. Both a and b
  4. none

Answer: b

Q4. Life would become slow without which ATP production?

  1. Fermentation
  2. Glycolysis
  3. Mitochondrial
  4. Both a and b

Answer: c

Q5. The end-product of glycolysis, pyruvate entered into which process?

  1. Krebs cycle
  2. Citric acid cycle
  3. Electron transport chain
  4. Both a and b

Answer: d

Q6. During aerobic respiration, free oxygen accepts electrons and reduces to water.            True/false

Answer: True

𓇼 Krebs Cycle Steps:

Q7. Who discovered Krebs Cycle?

  1. Schleiden
  2. Robert Hooke
  3. Leeuwenhoek
  4. Hans Krebs

Answer: d

Q8. When Krebs cycle was discovered?

  1. 1927
  2. 1928
  3. 1930
  4. 1932

Answer: c

Q9.Which is a series of reactions in which pyruvate entered from glycolysis?

  1. Lactic acid fermentation
  2. Alcoholic fermentation
  3. Electron Transport Chain
  4. Krebs Cycle

Answer: d


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Q10.During Krebs Cycle, the pyruvate is oxidized to which molecule?

  1. Oxygen
  2. Carbon dioxide
  3. Nitrogen
  4. Hydrogen

Answer: b

Q11. In the Krebs cycle, two electron carriers act as hydrogen acceptors.        True/False

Answer: True 

Q12. Which are the two electron carriers act as hydrogen acceptors during Krebs cycle?

  1. NAD
  2. FAD
  3. NADH
  4. Both a and b

Answer: d

Q13. How many molecules of CO2 are generated from each pyruvate molecule during the reduction of NAD to NADH and FAD to FADH2?

  1. Three
  2. Four
  3. Five
  4. Six

Answer: a

Q14. The molecules NADH and FADH2 once reduced are transferred into the electron transport chain.    True/False

Answer: True

Q15. The pyruvate is first changed in acetic acid.          True/False

Answer: False (Acetyl CoA)

Q16. Which is first enters into the Krebs cycle?

  1. Pyruvate
  2. Acetyl CoA
  3. NADH
  4. FADH2

Answer: b

Q17. During step one of Krebs cycle, Acetyl CoA  adds its two-carbon fragment to oxaloacetate.       True/False

Answer: True 


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Q18. Which is a four-carbon compound?

  1. Citrate
  2. Isocitrate
  3. Oxaloacetate
  4. None

Answer: c

Q19. When acetyl group is attached to oxaloacetate, which product is formed?

  1. Isocitrate
  2. 6-carbon citrate
  3. Fumarate
  4. Malate

Answer: b

Q20. In step-2 of Krebs cycle, a molecule of water is removed and citrate is converted to its isomer______________.

  1. succinate
  2. malate
  3. isocitrate
  4. succinyl CoA

Answer: c

Q21. During step-3, substrate loses a CO2 molecule and the remaining 5-carbon compound is oxidized and it reduces NAD to NADH and which product formed?

  1. succinate
  2. malate
  3. succinyl CoA
  4. a-ketoglutrate

Answer: d


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Q22. In the step-4 of Krebs Cycle, which product is formed when CO2 is lost and now 4-carbon compound is oxidized and it reduces NAD to NADH and then compound is attached to coenzyme?

  1. succinate
  2. malate
  3. succinyl CoA
  4. none

Answer: c

Q23. Substrate level phosphorylation occurs in the 5th step of Krebs cycle.       True/False

Answer: True 

Q24. When CoA is replaced by a phosphate group, the phosphate group is then transferred to GDP which forms _______.

  1. NAD
  2. FAD
  3. GTP similar to ATP
  4. Both a and b

Answer: c

Q25. During step 6 of Krebs cycle, 2-hydrogens are transferred to form FADH2 which produces ___________.

  1. succinate
  2. fumarate
  3. malate
  4. citrate

Answer: b


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Q26. Bonds in the substrate are rearranged by the addition of a CO2 molecule and malate product is formed during step-7 of the Krebs cycle.    True/False

Answer: False (addition of a water molecule)

Q27. In the step-8 which is the last step of Krebs cycle, another molecule of __________ is produced?

  1. Pyruvate
  2. Acetyl CoA
  3. NADH
  4. FADH2

Answer: c

Q28. During the last step of Krebs cycle, NADH regenerates oxaloacetate, which is ready to enter into another reaction.

Answer: True 

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